It is well known that component sizes in integrated circuits (ICs) are decreasing, as articulated by Moore's Law. As component sizes decrease, it is increasing important to measure spatial profiles and linewidth roughnesses of structures in ICs, including MOS transistor gates, photoresist patterns, contact and via holes and interconnect trenches. Practitioners of IC fabrication metrology recognize that as structure sizes decrease, it is more difficult to measure profiles and linewidth roughness. There are several techniques in use; each has limitations. Transmission electron microscopy (TEM) is a destructive technique, and has a high sampling uncertainty due to limited throughput. Scanning electron microscopy (SEM) provides limited profile information. Scatterometry requires dedicated test structures and independent calibration.
Atomic force microscopy (AFM) overcomes many of the limitations of other metrology techniques discussed above, but, as currently practiced, has some limitations that prevent it from providing complete profile and linewidth roughness information. AFM uses a probe tip to determine a position of a point on a surface of a structure being measured. Tips in current use with rounded ends, such as the “tripod” tip, typically with radii of approximately 5 nanometers, cannot provide profile information in corners of structures, for example intersections of MOS transistor gates with gate dielectrics or active areas, where radii of curvature of structures may be less than 2 nanometers. Moreover, during use of a tripod tip configuration to profile an intersection of a vertical surface and a horizontal surface, it is uncertain which tip of the tripod is making contact with the horizontal surface, thus generating uncertainty in the measurement data. Tips in current use with tapered ends, such as “flare” tips, typically have vertical offsets that prevent profiling of the same corners discussed above. Both flare probes and tripod probes are too large to measure profiles of many contact holes and via holes. Tips in current use with wide ends to increase sampling area, such as square flare tips, require alignment and suffer from adhesion to IC surfaces. AFM techniques in current use that utilize sharp tips and rely on a known, controlled angle between the tip and the measured structure are prone to measurement error, and cannot accurately measure profiles of many via holes or contact holes.